This invention relates to a method of providing a pigment/binder type electrophotographic coating and compositions for such a method.
Pigment/binder type electrophotographic coatings generally refer to those comprising a photoconductive pigment dispersed in a binder such as an insulating resinous material. Such coatings are described in detail, for example, in U.S. Pat. No. 3,121,006. These coatings can be prepared by coating on a conductive backing a mixture comprising a photoconductive powder, a binder resin and solvent for said resin, followed by drying the coated mixture to evaporate the solvent. When the coating thickness is about 10 microns, the drying is completed in about 2 hours at room temperature. However, in order to insure a coating having satisfactory electrophotographic charge retaining properties, drying at an elevated temperature is recommended.
In the case of electrophotographic paper, such as Electrofax, which is used in document copying, and which is manufactured by paper manufacturers under controlled conditions, enforced drying may be carried out by the manufacturer without any difficulty. However, in the case of electrophotographic marking, utilizing electrophotographic marking paints, the end users of the paint must carry out coating and drying thereof on the material to be marked. Thus, enforced drying imposes upon the user an additional processing as well as an additional cost for suitable heating apparatus. Effective heating of materials to be marked is also a problem in that the materials are generally large in size, having enormous heat capacities, which also increases the cost of the marking operation. If heating is carried out by burning relatively low-cost crude petroleum, sulfur oxide compounds originating from impurities in the petroleum severely deteriorate the electrophotographic properties of the electrophotographic coating. Moreover, the installation of heating apparatus increases the potential of an explosion or fire during operation, since the electrophotographic marking operating requires various kinds of organic coating solvents, fixing agents, or in some cases, carrier liquid for development.